Automatic telephone-exchange system



Feb. 25, 1930. BRANDER AUTOMATIC TELEPHONE EXCHANGE SYSTEM 6 Sheets-Sheet 1 Filed Aug. 8, 1925 Feb: 25, 1930. B. BRANDER 1,748,538

AuToEA'rIc TELEPHONE EXCHANGE SYSTEM Filed Aug. 8, 1925 s Shets-Sheet 2 E/vi I ,B. Brawler Feb. 25, 1930. B. BRANDER AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Au Qs, 1925, e Sheets-Sheet' 6 qm w wow n w WoN Feb.' 25, 1 930. I BRANDER 1,748,538

AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Aug. 8, 1925 s Sheets-Sheet 4 en, v

F 25, 1930. B. BRANDER 197485538 AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Aug. 8. 1925 6 Sheets-Sheet 5 E 8. m2 g b .N .Hr um n2 mow m R m H w H E f 2 J o o m 2.. N E N E 2 2w m h .vlw 2. SN

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AUTOMATIC mmrnoum EXCHANGE SYSTEM Filed Aug. 8, 1925 6 Sheets-Sheet 6 Patented Feb. 25, 1930 BERTIL BRANDER, OF STOCKHOLM SYVEDEN 7 AUTOMATIC TELEETl-IONE-EXCHANGE SYSTEM Application filed August 8, 1825, Serial No. 49,094, and in Sweden May 31, 1924.

This invention refers to "an automatic telephone exchange system and particularly to automatic switchboards of a new type for such exchanges in connection with a special calling or number sending device for the subscribers instruments.

In this system the selectors are carried out in the form of small carriages running on hor izontal rails, each carriage or selector being provided with a miniature electric-motor, which simply drives the selector along its track forwards and backwards. The'c-onnection for the motor current is established by means of a sort of trolley making contact witl1 conductors runiiing along the track. The connections to the various telephone or trunk lines is made by means of asliding C011,

tactarm on the carriage which gets its connections by means of separate rollers and leads along the track in the same way as the motor. The contact arm in its various positions of the selector makes connection with the lines by means of vertical conductors, three for each line, provided with lugs or projections against which three brushes on the contact arm are sliding.

The invention further comprises a number sending device at the subscribers instrument, especially designed for the cooperation with selectors in this system. r

In the accompanying drawings is represented a telephone system according to this invention. H

Fig.1 is a plan, Fig. 2 a front view and Fig. 3 a side view of a selector.

Fig. 4 shows a diagram of the subscribers instrument. Fig. 5 shows the circuit diagram of aline finder, F 6 the circuit diagram of a group selector and Fig. 7 the circuit dia-;

gram of a connector.

Fig. 8 is a diagram of a modified line finder arrangement.

The selector shown in Figs. 1-3 mainly consists of a small three phase motor M, provided with a synchronously rotating armature 35,and arranged to move easily on two small wheels 1, 2 on a rail 5, like a carriage, while it is guided by means of two rollers 3, 4 which engage with a downwardly project- 50 ing edge of the carrying rail 6 for'the next selector above the one shown in the drawin 'The triangular iron frame 34 of the motor carries the three field coils 33 and the two pole armature 35 is provided with a single coil 39 for polarizing the armature by means of continuous current. The armature 35 is provided with a hollow shaft 36 which revolves on a fixed pin or pivot 37. The shaft 36 carriesa pinionl38 engaging with teeth at the front side of the rail 5. The armature coil 39 has one end connected to the body 35 and the other end to an insulated pin 40 at the top end of the armature shaft 36. An insulated spring 41 fixed to the frame 34 presses against the pin 40 and forms one of the connections of the coil 39 to the external circuit, the second connection'being formed by the pivot 37 and the frame of the motor.

The motor frame 34 further carries a kind of a trolley, composed of six rollers 13 to 18 insulated fromeach other and from the frame. and making contact with six insulated con ductors in the form of rails'or strips 19'24. Three of these conducting'rails 22, 23,. 24

carry the three phase current to the motor magnets 33 while the other three rails 19, 20, 21 form the connection to three insulated brushes 7, 8, 9 mounted on the contact arm K of the selector. The contact arm K is mounted between pivots in a bracket 26 (Fig. 3) fixed to the mot-or frame 34. The contact arm K is movable a small angle round the'pivots, whereby the brushes 7,8, 9 may be swung outof contact with the multiple bank. This is effected when the selector is moving with its highest speed, by means of a centrifugal deviceC. This device contains two weights 29, fixed to springs 30,'one end of which are fixed to the hollow spindle 28 of the wheel 1, while the other end of the springs 30 are fastened to a pin 31, which moves axially through the spindle 28. Thus the weights 29, when the selector moves very fast, rotate quickly and are thrown outward by the centrifugal force, thereby pressing the pin 31 inwards so that the latter will press on the inner end of the contact arm K causing its outer end with the brushes 7, 8, 9 to be swung out from the bank. 1 The centrifugal device C is however so adjusted that, when the selector moves with a certain slower speed, the pin 31 does not touch the contact arm K, a spiral spring 32' in this case holding the brushes 7, 8, 9 tight up against the bank contacts 10, 11, 12.

The bank or multiple contacts 10, 11, 12 are in the form of metal strips with lugs projecting towards the brushes, as shown in Figs. 1 and 3.

Three of these strips are provided for each line, of which two belong to the talking circuit and the third to the test circuit.

The contact rollers 1318 are each composed of two pressed halves of thin sheet metal, which are held and pressed together by means of two springs 25, these springs at the sametime forming the electrical connection to the rollers. The two halves of the rollers are not in any way fixed together, but each half can revolve freely and it is pivoted in the spring only by means of a pressed up nipple fitting into the hollowness of a similar nipple of the spring 25. These contact rollers engage with the contact rails 19 24 in such a manner that each roller grips the rail tightly between its two halves, thus forming a reliable (double) contact with only slight wear of rubbing surfaces.

From the foregoing description of the selector it will be understood that, properly speaking, the selector is composed of two main parts, namely the fixed'track with its rails, and the carriage or selector proper which acts as a sliding contact arm. In the following description of the operation of the system, however, the movable carriage, for sake of shortness, is called the selector.

It is obvious, that the line capacity of this selector may be varied within wide limits, because the construction of the movable part of the selector is of course not in any way depending on the length of the track. Thus, this selector may be made for any-desired number of lines, for instance 1001000 lines, provided that the carriage is arranged to run fast enough, so that the switching operation can be completed in a reasonable time. For this reason, if the selector is arranged for a large capacity, for instance 5001000 lines, it is given a faster motion when selecting groups, for instance 100-150 steps per second one step expressing the distance the selector must move from one set of multiple contacts to the next set-while for the selection of an individual line in the groups a speed of only 30-40 steps per second may be used. To avoid excessive wear of the sliding brushes and multiple contacts during the faster motion of the selector, the above men tioned centrifugal device C holds the brushes out of contact with the individual lines during the faster motion.

The operation of the selector will be clearly understood from the following description of the circuit diagrams, which represent the switches of an automatic exchange for 10000 subscribers lines. The capacity of the line finder, Fig. 5, may be 5001000 lines and the group selector, Fig. 6, 500 lines-10 groups of lines. The capacity of the connector in consequence will be 1000 subscribers lines.

Fig. 4 shows the diagram of the subscribers instrument A including the number sender.

The circuits for talking and ringing in this instrument may be of any kind generally used for common battery working.

The number sender consists mainly of a switch arm 50 in connection with a spring driven wheel-work.

The switch arm 50 is fixed to a toothed wheel 56 and a clock spring has one end fixed to this wheel 56 and the other end to a crank 01 for winding up the spring. The wheel 56 engages with the pinion of a second wheel 57 engaging with a pinion 58 on the shaft of a thin, blade-shaped steel magnet NS mounted on pivots between the poles of an electro-magnet 59 so that it may freely rotate when the electromagnet 59 is not energized. The switch arm 50 normally rests on a contact-55 and in this position it closes the circuit of the speaking set A across the branches 65, 66 of the subscribers line, but when the arm 50 is setin rotation by turning the crank 61 one turn round, it leaves the contact 55, thereby interrupting the circuit of the speaking. set A, and then slides successively over four contact segments 51, 52, 53, 54 and then stops again, after one revolution. on the normal contact 55.

The contact segments 515d are arranged in such a manner, that their active contact surface may be individually varied to different lengths by means of a turning knob or any kind of a handle moving over a scale with the divisions marked with numerals or letters according to the adopting numbering scheme. To effect the variation of the active contact surface of the segments til-5 these segments may have a concentric movement, whereby they will be more or less covered by fixed insulating segments of some thin material.

Fig. 5 is a diagram showing the relays in connection with the subscribers line in the central exchange and the'circuit of a line finder.

The subscribers line 65, 66 is connected to contacts 67. 68 in the multiple contact field of the line finder and one branch is further connected to one winding of a combined line andcutoff relay 70 and a pilot relay 71, which is connected to the earthed plus pole of the central battery, while the other branch 66 is connected to the minus pole of the battery through a resistance 72. The corresponding test contact 69 in the multiple field is connected to a contact 73 of the line relay 70, which when energized extends this circuit to the minus pole of the battery through a sec- 0nd winding of the relay, 70. This relay is adjusted insuch a manner that its armature onlycloses the contact 73 when it is excited only by the current in the line and its left hand winding, which has a high resistance; butwhen a local circuit is closed through its right hand low resistance winding, it becomes more powerfully excited andthen also opens the two other contacts, thus cutting itself and the battery oif the line.

The pilot relay 71 is common to a certain numbeig for instance 100 lines," and its purpose is,by the aid of a secondary pilot relay 74, to start a number of line finders provided for the groups of lines in question.

The line finder differs mechanically from the selector shown in Figs. 13 with regard to the centrifugal device C, Fig. 1,which is omitted inthe line finder,because the latter is arranged in such a way that it has no derinite normal position but simply stops at the contacts where it was lastly used. It is therefore not necessary to give the line finder the high speed, as there will always be some line finders in theneighbourhood of the calling line. On the other hand, the line finder is provided .with a switch80, Fig. 5, which is actuated by means of a fixed stop or projection at each end of the track in such a manner that it changes its position every time the line finder reaches one end of the track, wherebytwo phases of the three phase current are changed, causing the motion of the motor to be reversed. I

According to the diagramsshown in Figs.

4-7, which of. course only serve as an example 7 of a suitable way of carrying out the inven-' tion, the operations of the line'finder and the group selector are controlled only by means of relays, while for the operation of the final selector a sequence swltch is used in con unction with some relays.

To facilitate the understanding of the diagrams and the operation of the switches a short explanation of the method of handling the subscribersinstrument and the number sender may be advanced, particularly because this method somewhat deviates from the ordinary course.

1. The subscriber sets the desired number by turning the contact segments of the number sender in accordance withthe figures of.

the number, then'he starts the number sender by turning the crank once round, all while.

that the wanted number is being rung up or that it is engaged. But if the subscriber prefers it, he need not immediately remove the receiver but he may wait till the bell rings,

which is a sign that the connection to the: I desired line'is completed and that the hue 1s not busy, and when he now lifts the receiver In the latter case the whole chain of switches, v

used for setting up the connection, after a few seconds are automatically restored to their normal positions.

3. In order to renew a call it is, of course, only necessary for the subscriber to again wind the spring of the number sender.

The operationof'thesystem is as follows Supposing a subscriber wants to call No. 5280. @He sets the number sender accordingly, and the contact segments 51-54, Fig. 4, will then have the positions or proportionate lengths shown in the figure. Next he turns the crank 61 once round, thereby winding the spring 60, atthe same time releasing the switch arm 50, which leaves the normal contact 55 and passesover to the segment 51. (The mechanical details of the release and interlocking arrangement of the switch arm 50 and the crank 61 will be the subject of a separate patent application.) Meanwhile thearmature NS revolves freely, only acting as a mechanical brake, because there is no current flowing through the windings of the electromagnet 59. But as soon as the switch arm 50 reaches the segment 51 a current is closed through the electromagnet 59 which now retains its armature and stops the motion of the switch arm 50. The circuit of this current is: plus pole of the central battery (earth) 7 1-'7 0'6550515966 72minus pole. This current energizes the line relay 70, which closes the contact 73 but does not yet open its breaking contacts),

. thereby connecting the multiple test contact the right hand 'bar 82, from which branching wires 83 lead.

to the'starting relays 81 of a number of line finders. All those relays 81, which belong to vacant linefinders, will thus be energized. Circuit of each start relay 81: Earth75 838185-minus pole. I

The relay 81 closes, by means of its contacts 87, 88, 89, the three phase current from a generator Gr over the winding of three polarized relays 95, 96, 97, the normally closed contacts of a test relay 82- and the field coils 91, 92,93 of the motor M. At the same time a continuous current is closed through the armature coil 94 from the battery B. Further relay 81 puts earth potential on the test brush 98 over the contact 99 and the test relay 82.

Thus all vacant line finders, provided for the group of lines in question, are started and the one, whose test brush 98 first comes in contact with the test contact 69 of the calling line, will stop on this line, because the test relay 82 will be energized in series with the cut off winding of the relay 70. As this relay winding has a comparatively low resistance the relay 70 will at the same time be more powerfully excited and will therefore pull up its armature fully, breaking the two normally closed contacts.

The test relay 82 beingenergized cuts off the three phase current to the motor M, but at the same time it closes a direct current through one (or two) of the field coils 91, 92, 93 in series with the armature coil 9 1 and the left winding of the relay 8 1. This current is taken from the central battery, which has ahigher voltage than the generator G and the battery B, and as the said winding of the relay 84 has a low resistance, it will be stronger than the currents for driving the motor. It has however only a short duration, as will be further explained below, the purpose of this current being only to stop the motion of the motor armature as quickly as possible and to pull it back in such a position that the brushes of the contact arm K will coincide properly with the multiple contacts 67, 68, 69 of the calling line.

The adjustment of the position of the line finder w'th its contact arm K in relation to the multiple field contacts 67, 68, 69 is ef fected by means of the motor and the polarized relays 95, 06, 97, which during the working of the motor M vibrate in synchronism with the alternating currents. hen these currents are interrupted, the armatures of the polarized relays 95, 96, 97 remain in the positions they had just in the breaking moment and in consequence one or two of their contacts 102, 103, 10 1 will remain closed after the break of the three phase current. It is thus obvious that the continuous current from the central battery will be closed over one or two of the contacts 102, 103, 104 in series with the corresponding contact or contacts of the three closed contacts 99, 100, 101 of the test relay 82 and the left winding of the relay 84, and this current (or these currents) will excite the field and armature coils of the motor M in such a manner that the armature will take up the same position it had in the moment the three phase current was broken. The relay 84 is consequently energized at the same time and by opening its contact it cuts off the current for the start relay 81. The latter relay is however arranged with a slow acting release, so that it keeps its contacts 87, 88, 89, closed a short time-for instance half a second-after the opening ofthe contact 85, and during that interval the setting of the motor armature, efiecting the adjustment of the contact arm K on the field contacts, is completed.

The relay 84, when energized, also closes three contacts 86, 105, 106 by which the con- (luctors 107. 108. 109 leading from the three brushes of the contact arm K are extended to the group selector, Fig. 6. At the same time a new circuit is formed for holding the relays 70 and 8 1: eartha resistance 110 (Fig. 6) 8t861099869-7870minus pole. lVhen subsequently relay 81 releases its annature and opens its contacts, this does not interfere with the holding of the relays 70 and 8 1, but by the release of the relay 82, which follows on the opening of the contact 90, the

setting current in the motor coils is broken.

At the above mentioned closing of the relay contacts 105, 106 a new line circuit is formed at the moment of cutting out the line relay 70 from the subscribers line, through the winding of a starting relay 117 for the group selector as follows: central point of the common battery CB (Fig. 6)111105 10767-6550-515966-68 108 106 112 117 CB, minus pole. Thus the electro-magnet 59 of the number sender remains excited, still retarding the wheel work, but the starting relay 117 is now also energized. This relay closes by the contact 118 the circuit of a relay 119, which by its contacts 120, 121, 122 closes the three phase current to the motor M of the group selector. This three phase current is however not taken from the generator G, Fig. 5, but from another generator, supplying a current of a higher frequency, say 2030 periods per second, while the generator G may give a current of only 510 periods.

The battery B, Fig. 5, is also connected to the central point of the winding of the generator for the higher frequency.

Thus the armature coil 123 of the group selector motor M is polarized by'the continuous current iirtlie same way as the armature of the line finder motor and will rotate in synchronism with the phase. On account of the high speed of the motor the centrifugal device (Fig. 1), which is provided in this selector, will come into action and turn the brushes 12 1, 125, 126 of the contact arm K out of contact with the multiple. One of the brushes, 126, will however during the fastei motion of the selector slide on a number of special, earthed contacts 130, which are standing out of the surface formed by the multiple contacts and may have an extended contact surface as indicated in Fig. 6. These contacts 180 are provided for the purpose of sending arr-impulse to the number sender every time the selector passes into a group of trunk lines. Thus there will be 10 impulse contacts 130 for each group selector track, as in the example there are 10 groups of trunk lines leading to final selectors.

When the group selector leaves its normal position a switch 181 is released, which closes two contacts 132, 133 as a preparation for subsequent functions.

When the brush 126 during the motion of thegroup selector comes in contact with the earthed contact 130, the earthed plus pole of the central battery GB is directly connected to one branch of the subscribers line by the closed contact 1340f the starting relay 117, which results in the tollowingline circuit: earth130-125134112+10610868 66-'595150-G567+107105111 CB (central point) In consequence the current in the subscribers line is reversed when the brush 126 touches the Contact 130, but is restoredto its original direction again as soon as the brush 126leaves the contact 130.

gearing of the wheel-work, Fig. 4, is carried out, in such a manner that the switch arm.

moves onestep.corresponding to one unit of every figure in the recorded number-for every complete revolution of the armature N-S. 'Thus, when the group selector has passedfive groups ofline's, the switch arm 50 of the number sender will stand at the bottom of the segment 51 and when the group selector enters the sixth group, the switch arm 50 will leave'this segment and break the current in the line and the magnet59. In consequence the wheel work will no more be retarded by the magnet, but the switch armsis moved on bythe driving spring, while the armature NS again acts as a mechanical brake, until the switch arm 5O comes incontact with the next segment 52, whereby the line current is'again closed through the mag- 1 net 59. During this momentary interruption of the line current, the relay 117, Fig.6, re.-

leases its armature andshort circuits by its normally closed contact 135 and the previously closed contact 132 or the off normal switch 131 its own winding, which short circuit prevents the relay 117 to come into action again until the selector has returned to zero.

Thehne current is thus (somewhat increased in strength) again closed through the magnet 59, Fig. 4, as soon as theswitch arm 50 reaches the segment '52, as already mentioned, wherebythe wheel work is again reta'rdedbythe magnet 59.

By the release of the relay 117, Fig. 6, its contacts 118 and 134are opened, the former opening the circuit of the relay 119, which in turn opens its contacts'120, 121, 122 and cuts :oii'the' three phase current 'of'the higher trequency from the motor M of the selector, while the latter contact 134 cuts oil the connection between the relay 117 and the brush 126. At the same time a current is closed from earth by the contact 136, the previously closed contact 133 of the oil normal switch 131 and the normally closed contact 140 of a relay 139 through the winding of a relay 137, which is further connected to the minus pole by a normally closed contact 141 of a relay 138. 7 It will be noticed that the winding of the relay 138 is at this moment-connected in parallel with the relay 137, but asthe latter relay has a winding of alowerresistance,giving considerably more ampere-turns, than the winding of the relay 138, it will pull'up its armature much quicker thanthe relay 138,

whichin consequence will be cut out by the contact 142, before it has had time to pull up its armature.

The relay 137 closes by its contacts 143, 144, 145 three phase current of the lower frequency from the generator G,-Fig. 5, to the motor M of the group selector, which now will continue its motion at a reduced speed over the multiple contacts or the sixth group. Ow-

ingto the-lower speed of the'selector, the

centrifugal device C, Fig. 1, will in this case I not have any influence on the posltion of the contact arm K and its brushes, which in consequence will slide on all the multiple contacts 127, 128, 129 of the group. i I The threeph ase current of the'lower frequency, as in the case of the line finder, is passing through the windings of three polarized relays-147, 148, 149 tor-the adjustment ot. the position of the selector when stopped. 1 The relay 137,- when excited, connects by the contact 146 the test brush 126 ofthe selector'with the minus pole of the battery through the ri ht windin of the test rela V D F;

139 and a resistance-155. When the test brush 126 makes contact with the test contact 129' of a vacant trunk line, the test relay 139 will become excited and will break the supply of three phase current at the contacts 150,151, 152, at the same time connecting the windings of: the motor Mto the contacts of the polarized relays 147, 148, 149, cutting off the current to the relay 137 at the contact 140 and earthing the resistance 110 by the contact 153, which substitutes this earth connection for the normally closed contact 113 of the relay 116 when this relay, a moment later, pulls up its armature. The circuit of the test relay 139 is traced as follows: earth-contact 164 or the sequence switch of the final selector, Fig. 7,resistance 163.162-129126- 139-1 146minus pole. 7

When the three phase current 1s cut 011 by the test relay 139, the polarized relays147,

148, 149 will retain their armature in the positions they had at the breaking moment and by the one or two of its contacts, which thus remain closed, battery current will flow throughthe motor coils and adjust the position of the sel-ector'in the same manner-as described Withregard to the line finders. The

said battery current also passes the winding of the relay 116, but this winding is for a moment shunted by the left winding of the relay 139, which has only a low resistance, and -for this reason the relay 116 can not at once pull up its armature. The cause of the left winding of the test relay 139 remaining for a rtaneously with the break of the contact 1 10 of the test relay 139, but by the slow release of the relay 137 the shunt will remain in circuit say one half second, which is suflicient for the adjustment of the selector brushes to their proper position on the multiple contacts. After that interval the above mentioned change in the relay circuits will take place. The said shunt is carried out as a winding of the test relay 139 for the purpose of holding the relay in case the motor no sooner can be stopped than the brush 126 has left the test contact 129 and then is brought back again by the adjusting current. It the multiple con tacts and the gearing of the motor arranged in such a manner that one revolution of the motor armature carries the selector six steps motor.

By cutting out the shunt of the relay 116 the current in this relay, which has a high resistance, will be as much increase-d that the relay will pull up its armature, thereby disconnecting the line from the battery GB at the contacts 111, 112 and extending the line circuit, by closing the contacts 11%, 115 to the brushes 12 i, 125 and further to the connector, Fig. 7. The relay 116 also opens the contact 113, which however has no immediate influence on the circuits, because this contact is bridged by the contact 153 so long as the test relay 139 remains active, but it will serve to release the line finder when the test relay 139, at the end or" the conversation, is cut out by a break of its circuit at the connector.

' When the relay 138 is energized it closes a contact 156 for holding the relay 139 in place of the contact 146 and at the same time to in crease the minus potential oi the multiple test contacts 129 by cutting out the resistance The contacts 15% and 156 are arranged in such a way that 156 is closed before 15 1 is opened, in order to prevent the relay 139 from falling back through any momentary break of the holding current.

The principal function of the relay 138 is to restore the group selector to its normal po- 8113011213518? the conversation, or if the desired line is engaged. F or this purpose it closes three contacts 157, 158, 159, by which three phase current of the higher frequency flows to the motor when the test relay 139 is released, and closes its contacts 150, 151, 152. It will be noticed that, in this case, two leads for the phase current are exchanged, in order to reverse the motor and drive the selector backwards to its normal position. Having reached its normal position, the selector strikes against the switch 131, which opens its contacts 132 and 133, the latter contact breaking the holding circuit of the relay 138.

For the connector, Fig. 7, there is provided a sequence switch, which in conjunction with some relays is used for controlling the movements of the connector and other operations in connection with same.

The designot the sequence switch is quite optional. It may be of the well known power driven type or it may have an ordinary stepb-y-step drive. In Fig. 7 the driving mechanism of the sequence switch is represented by an electro-magnet 168, and for the understanding of the circuits and operations it is sufficient to presume that all the switch arms of the sequence switch are moving simultaneously and with a constant speed, as soon as the magnet 168 is energized. The numerals at theswitch arm contacts indicate the positions in which the respective contacts are closed. 7

For sake of shortness the sequence switch is in the following description called only switch and the sequence switch arms only switch arms.

In the example of the system, represented in the drawings, the connector has a held of multiple contacts for one thousand subscribers lines, which are divided in ten groups of a hundred lines, while each of the 100-line groups is again divided in ten groups of ten lines each. It is obvious that the connector may be carried out for some'other capacity for instance 500 lines, in which case the length of the connector track of course is reduced to one half of the track for 1000 lines.

When the group selector, Fig. 6, has found a vacant connector, Fig. 7, the subscribers line is with one branch 160 connected to the central point of the common battery, in Fig. 7 indicated with and with the other branch 161 to the minus pole of the battery through a starting relay 167, as in the case of the group selector. The line circuit is then as follows: central point oi the battery )165160 12712 1114l10510767655052 596668108106115125128161 166167minus pole or" battery.

' The starting relay 167, in consequence, is energized and closes by its contact 169 a current to the switch magnet 163. Circuit: earth169-1701681ninus pole of battery. Thus the switch starts moving all its switch arms, but when they arrive to posiand the switch arms 17 e,

tion 1, the arni170 b eaks the circuit of the magnet 168 and the switch stops in this position. The relay 167 has further closed three contacts 171, 172, 173 and by these contacts 17 5, 176 threephase current of the higher frequency is closed to which is connected to earth.

the motor M of the final selector from the supply circuit X, Y, Z.

During the fast motion of the connector the contact arm K with its brushes 177, 178, 179

is turned out of contact with the multiple contacts 180, 181, 182' of the lines in the same manner as described with regardto the group selector, but the test brush 17 9 slides on two kinds of impulse contacts, namely one contact 183 at the beginning of every'group of hundred lines, which is vconnectedto the minus pole of the battery, and one contact 18 1 at the beginningofevery group of ten lines, The test brush 1 179 is connected to a relay185, which by the switch arm 186 in the position 1 is connected to earth. p p

When the connector starts and enters the first groupiof lines, the brush 179 will make contact with-the first impulse contact 183 and close thecircuit of the relay 185, which closes a contact 187, thereby earthing one branch 161 of the line. This will cause a reversal ofvthe line current 1n the same way as described with reference to the group selector, while the starting relay 167 remains energized. Owing to thereversal of the line current the magnet 59 of the number sender, Fig. 1, will change its poles, its armature will make hall a turn and the switched arm will move half a step forward on thesegment 52, The line current is again reversed when the brush 179 leaves the im- 'pulsecontact 183 and the switch arm moves another half step. The brush 179 then slides over all the earthed impulse contacts 184 for the decades, but this has no influence on the relay 185, because it is still connected to earth by the switch arm 186. The same procedure is repeated when the connector enters the second rou of hundred lines. the switch 1 arm 50-then moving another step. But when the connector enters the third'hundreda mo mental-y break of the line current takes place while the switch arm 50 is going over from.

the segment 52 to 53,1and this causes the 170 drivins 't 1e switch in the osition 2..

relay 167 to release its armature for a mo-.

ment. During this interval the three phase current iscut off at the relay contacts 171,

172, 173, the continuous current is closed through the motor coils by the contacts 189,

190, 191-in this case not for the purpose.

of adjusting the position of the selector but only to act as a brake on the motor-and a current is sent through the switch magnet 168 by the contact 188 and the switch arm The switch arm 170, in moving to the position 2, again breaks the circuit of.

the magnet168, but when the relay 167 at the arrival of the switch arm 50 to the seg ment 53 is again excited, it closes the same three phase circuit againand also the circuitof the switch magnet 168 by the contact 169 and the switch arm 170, driving the switch vin the position 3.. ,The current for braking the motor passes through a differentially wound relay 200, the function of which will be explained below. v

The connector now continues its motion forward, but when the switch moved from position 1 to 2, the impulse relay 185 was switched-over from earth to the minus pole of the battery by the switch arm 186,, the

latter connection remaining also in the position 3 of the switch. 7

When subsequently the brush 179 of the contact arm K passes the impluse contacts 184, the relay 185 will receive an impulse for each of the contacts 1841 passed the brush and this will result in as many impulses being sent to the number sender in the same way 'as described before. According to the example of the number re corded in the number sender, the switch arm 50 willthus move nine steps by the decade impulses and, at the ninth step, it

will leave the segment 53 and again break the line current, The starting relay 167,,

the relay 185 is switched over from the minus pole of the battery to ts central point-- v marked by means of the switch arm 186. The starting relay 167 is again excited, as soonas the switch arm 50 of the number sender has reached the segment 54, and the relay contacts 171, 172 173 are thus again closed, but the motor M does not receive the driving, current again, before the switcharms 17 1, 175, 176 arrive in position 5. In-

the meantime the closing of the relay contact I 1.69 putsearth on the branch 161 of the line,

causing the line current to be reversed and the switch arm 50 of the number sender to move half a step. Further when the brakingcurrent the lasttime is closed to the motor by the relay contacts 189, 190 01- 191 via the switch arms 192,193 or 191 and the relay contacts 195, 196 or 197, this current passes throughthe differentially wound re lay 200 and excites this relayin a way explained bel0w'so that it opens its contact 216, and when the relay 167, asalready mentioned, is again excited, interrupting the braking current at the contacts 189, 190, 191,

the relay 200 is (slowly) released and closes a current by its contact 216 via theswitch arm 215 to the switch magnet 168 causing the switch to move to position 5. In doing so, the switch arm 2&6 breaks the earth connection via the relay contact 169, causing the switch arm 50 of the number sender to move another half step.

It will be understood that the arrangement of the switch arm 2&6 in connection with the relay contact 169 serves to send an extra impulse to the number sender on account of the fact that the connector stops on the line following the opening of the line circuit when the switch arm 50 leaves the segment At the same time the switch arms 17%, 175, 176 in position 5 close the low frequency three phase current to the motor M via the windings of the polarized relays 201, 202, 203, and the connector, which has now arrived to the ninth group of tens within the third hundred, continues its motion at a slower speed, while the brushes 177, 178, 179not being influenced by the centrifugal device C slide on the multiple contacts 189, 181, 182.

During this motion of the connector the relay 185 will receive an impulse every time the test brush 179 passes over a test contact 182. The connection of the relay 185 to the central point of the common battery during this last motion of the connector is done to enable the relay 185 to receive the impulses from the test circuit of every passed subscribers line without regard to whether the line is busy or not. It the passed line is free, its test contact 182 has a minus potential through the right winding of the line relay 70. Fig. 5, in which case the impulse circuit will be: P -186'185'179-182-20 1 minus pole of battery. It a line is busy, its test contacts 182 are connected not only with the minus pole, as before said, but also, through a test relay, with the plus pole of the battery according to the, already in connection with the line tinder described and well known, method. of testing and marking a line busy. As the test relay 167 (right winding) has a low resistance, the test contact 182 of a bus line will have plus poten tial. The impu se circuit when passing a busy line will therefore practically be as follows: earthl69 (or 208)207167 (right wnding)-179182 (the preceding parts exist at the connector occupying the busy line, while the following parts are found at the moving connector)182179185 186 In order to prevent these impulses from influencing in any way the line relay 70 or the test relay 167, connected to a passed busy line, the impulse relay 185 is provided with winding 01 high resistance, for instance 2000 -3000 ohms.

When the connector has passed nine lines of the ninth group of tens, the number sendwas es er has received ten impulses since the switch arm 50 arrived to the segi'nent 5 1, and at the tenth impulse the switch arm 50 leaves the segment 5 1, interru ating the line circuit and continuing its motion by the force of the spring 60 until it arrives to its Zero position,

where it connects the subscribers speaking set A with the line by the contact 55.

At the lastinterruption of the line circuit by the switch arm 50, the relay 167 is released and by opening its contacts 171, 172, 173 it cuts cit the three phase current and by closing its contacts 189, 190, 191 sends the adjusting current through the motor coils. This current flows from earth through the armature coil 209 of the motor M, the field coil or field coils of same, which by one or two of the contacts 195, 196, 197 remain in the circuit at the moment the three phase current is cut oft, the winding 210 of the relay 200, shunted by the winding 211 in series with a resistance 213, to the minus pole of the battery. It will be understood that the winding 210 of the dilierentially wound relay 200 is in this case the active winding, the resistance 213 being very high compared with the resistanceot the relay windings 210, 211, which are equal with regard to resistance and number of turns. The relay 200 closes its contact 21%, thereby sending a current to the switch magnet 168 over the switch arm 215. Thus the switch moves to position 6, the said current being broken in this position by the switch arm 215.

The switch-arms 192, 193, 194 at the same time cut olf the adjusting current for the motor, but a switch arm 199 in moving toposition 6 serves to substitutethe broken earth connection for the circuit of the relay 200 by a resistance 198, so that the energization of the relay 200 is continued in position 6 of the switch.

The relay 200 is provided mainly to serve as a time relay, which function begins in the position 6 or" the switch. For this purpose the resistance 212 is carried out in the form of a very fine wire of copper or some other material with a high temperaturecoeiiicient of resistance and arranged in such a manner that it will not be damaged by being heated to a temperature or" 70"8O C. Further it is arranged for cooling quickly by the surrounding air,'as soon as it is not heated by current. The ohmic resistance of 212 is at a temperature of 10 to 20 C. somewhat lower than that of the resistance 213, which is made of ordinary resistance material, not changing its ohmic resistance preceivably when heated. Or the resistance 213 may consistof any material, it it is only arranged in such a manner that it is not heated materially by the current passing it. The ohmic resistance of 212 at ordinary temperature may be, for example,- 900 ohms while the resistance 213 measures 1000 ohms and each winding 210, 211 of the relay 200 about 1.00 ohms. r

The relay 200 begins to act as a time relay whenthe switch arm 199, in going from position 5 'to 6 opens ashort circuit of the resistance 212 and connects the resistances 212, 213 to earth through the resistance 198, the purpose of the latter resistance being only to regulate the time required for heating the resistance 212.

On account of the difference in the ohmic resistance of 212 and 218 the current in the relay Winding 210 will be about 10% stronger than in the counteracting Winding 211, and this difference is suiiicient for retaining the armature of the relay. The temperature of the resistance 212 will now gradually rise and after, for instance, 10 seconds its resistance has increased to about 1000 ohms. In consequence the relay 200 is demagnetized andits' armature falls back; i j

hen the switchmoves from the position 5 to 6 it further performs the following changes in the various circuit-s; j

1. The starting relay 167 is disconnected from the line by the switch arm 166 and the rightwinding of relay 167, whichis C0111 nected to the test brush on, one side, is on the other side connected to earth 'by the switch arm 207 through a resistance 208, for

the purpose ofconverting the starting relay 167 to a test relay. 1

2; The switch arm 170 connects the switch magnet 168 to the relay "contact 169 of the test relay 167.

8. The switch: arm 215 changes the connection of the switch magnet 168from the relay contact 214: to the contact 216.

4. The switch arm 165 changes the connection of the line branch 160 from the central point of the battery to the earthed left winding of an inductance coil 217. p

5; The switch arm 166, whenwdisconnecting the line branch 161 from the relay 167, connects said line branch 161 to'the windings' of the clearing relay 220 'for. the calling subscriber. r

6. The switch arm 218 connects the earthed right winding of the inductance coil 217 to a tone generator 219.

The connector is now standing on the multiple contacts 180, 181, 182 of the desiredsubscribers line No. 5280 and the next operation is to test whether this line is busy'or not. This is done by the relay 167 on the well known principle that the test relay, when 7 connected in series with the cut off relay of the desired subscribers line, will be suiiiciently energized to pull up its armature simultaneously with the cut off relay coming into action, if the line is free, while,.if the line is busy, the test relay can not pull up its armature, because it is shunted by another test relay. 7

If the line is busy, then the following functions take place: 1

The test relay 167 remains inactive and the time relay 200 keeps its armature attracted for about 10 seconds after the switch has arrived to the position 6, as already mentioned above. During this interval a busy tone is transferred to the calling subscribers line from the tone generator 219 by means of the coil 217. As mentioned above, the subscriber may now listen in his receiver and observe the busy tone, if he chooses to do so, or he maystill leavethe receiver on its support, the lifting of the receiver being of no influence on the switching operations when the desired line is busy.

When the'line relay 200 becomes deenergized .by the heating effect of the current in the resistance 212, its armature falls back and closes the contact 216,'thereby sending a current through the switch'magnet 168 and driving the switch to the position 7, where it stops owing to the said current being broken by the switch arm 215.. When going from position 6 to 7 the switch arm 164: breaks the direct earth connection to the resistance 163 and connects this resistance to earth over the contact 225 of the off normal switch 222, which closed the contact 225 when'the connector left itsposition of rest.

The switch arms 192, 193, 19 1, having arrived to the position 7, close the three phase current'of the higher frequency to the motor M, but in this case two of the phases (Z, Y) are changed and, in consequence, the motion of the motor is reversed and the connector returns home. Having reached its home position the connector stops against the off normal switch 222, which goes back to the position shown in the drawing, thereby changing the earth connection from the contact 225 to the contact 224. This opens the holding circuit for the group selector, which'will return to its'home position as-described in conmotion with the group selector.

At the same time the closing of the contact 224 sends a current over the switch'arm 223 through the switch magnet 168, driving the switch to position 8. From this position it is brought to position 9 by the closed contact 216 of the relay 200 and the switch arm215; from position 9 it is brought to position 10 by the closed contact 226 of the relay 220 and the switch arm 223, further to position 11 by the closed contact 233 of'the relay 230 and the same switch arm 223 and at last it is brought to its normal position 0 by the closed contact 224 and the switch arm 223-. k

It is thus obvious that, when the desired number is engaged, the connector, the group selector and the line finder all return to normal without any possibility of being kept engaged any longer by the subscriber.

As soon as the switch arrives to the position 6, the test relay 167 is energized in series with the line and out 01f relay 70 of the wanted line, both these relays pulling up their armatures simultaneously. At theclosing of the relay contact 169 the switch is now at once moved to the position 7 by a current passing said relay contact 169 and the switch arm 170. When going to position 7 the switch arm 207 cuts out the resistance 208 from the test circuit and connects the right winding of the test relay 167 to its own closed contact 169 for holding. But the switch does not stop in the position 7, because the relay 200 is still energized by the current passing the resistance 198 and the switch arm 199, thus the switch magnet 168 receives a current by the contact 214 and the switch arm 215, driving it to the position 8. In this position the switch arm 199 has changed the earth connection for the time relay 200 from the resistance 198 to direct earth over the closed contact 169 of the relay 167, and in consequence the resistance 212 now receives a stronger current and will therefore in a shorter time be heated to the temperature, at which the relay 200 releases its armature, the strength of the current being so adjusted that the said time will be 1% to 2 seconds. During this time an uninterrupted first ringing signal is sent out from the ring ing machine 240 by the switch arm 239. This ringing signal is however to begin with, sent out only over the calling subscribers line, if this subscriber has not previously taken his receiver from its support, and only when this is done, is said signal changed over to the wanted subscribers line. This operation is performed by the relay 220, which is energized by the transmitter current in the subscribers instrument. A condenser 246, inserted in series with the ringing machine prevents continuous current coming through the machine. The circuit of the said ringing current, in case the calling subscriber has not yet taken off his receiver is as follows: 240-- 24l6239228220 (right winding)166 16112812511510610868 66 A (the bell and condenser) 5065-67 1O71O5114:12 1128 160 165 217 (left winding)-earth240. It will be observed that this ringing current is partly shunted by the left winding of the relay 220 in series with the inductance coil 221, but the effect of the current passing this shunt is counteracted and practically neutralized by the main current passing the right winding of the relay 220. The two windings may have about the same number of turns, or the right winding may have fewer turns, depending on the inductance of the coil 221. Of course the main current in this winding will vary a little according to the resistance of the subscribers line, but this variation, owing to the high resistance of the condenser in series with the bell of the instrument, will be comparatively small and of no influence on the relay, which will remain inactive during the ringing until the subscriber takes the receiver ofi. When this is done, the battery current is closed through the subscribers transmitter and this current flows through the left winding of the relay 220, which now attracts its armature. At the closing of the transmitter circuit the ringing current in the right winding of the relay 220 is for a moment increased, which also contributes to the energization of the relay. By opening its contact 228 and closing 229 the ringing current is now switched over from the calling to the called subscribers line, passing a normally closed contact 231 of the called subscribers clearing relay 230 and the left winding of this relay, which neutralizes the effect of the portion of the current, shunted by the right winding and the inductance coil The circuit of the ringing current to the called subscriber is as follows: 240-246-239 229231-230 (left winding) -23817 8 '181205A (bell and condenser of the called subscribers instrument)206180 17 7237217 right 240.

This ringing current, in passing the right winding of the coil 217, produces by induction a similar, fainter current in the left winding of the coil 217, which flows through the receiver of the calling subscriber as a control signal of the ringing up of the called subscriber.

If the called subscriber does not at once answer. this first ringing tothe calling and the called subscribers will last altogether about 2 seconds, as mentioned above; after that time the time relay 200 will release its armature and send a current to the switch magnet 168 by the contact 216 and the switch arm 215, driving the switch to the position 9. in this position the switch arm 239 has cut the direct connection between the ringing machine 240 and the called line, and connected said line to an interrupter 241 for pcriodical ringing. At the same time the switch arm 199 has cut out the line relay 200, as it is not required any more for the present connection. The periodical ringing is now continued until either the called subscriber answers or the calling subscriber replaces his receiver.

\Vhen the called subscriber answers. l clearing relay 23 is energized in eXactl i th same manner as the clearing relay 220 el tl calling subscriber. When the relay 230 up its armature, the ringing current is cut or by the contact 231 and a current set to the switch magnet 168 by the contact 231 and t switch arm 227, driving the switch from posiwinding)earth tion 8-if he answers while the first-ringing current was sent out-or from position 9-if he answers during the periodical ringingto position 10, which is the speaking position. In this position the switch arm 239 has cut off the ringing machine from the relay contacts, the switch arms 24 2, 243 complete the connection between the subscribers line-and the switch arm 237 has connected the branch 206 of the called subscribers line to an inductance coil 236, forming the counterpart of the coil 235 for the supply of battery current to the transmitter of the called subscriber. Two resistances 244, 245 are inserted in the branches between the subscribers lines, in place of thecondensers, generally used for separating the direct current circuits of the subscribers lines. The resistances 244, 245 serve, to a certain degree, the same purpose, inasmuch as they prevent a too one sided flow of battery current in case of two lines of very different lengths being connected together, but at the same time they couple the relays 220, 230 together in order to prevent the clearing before both subscribers have re placed their receivers.

If the calling subscriber neglects to take his receiver off before the ringing signal, sent out in position 8 of the switch, is at an end, no more signal is transferred to the other subscribers line, as is easily understood from the diagram. and as soon as the time relay 200 is released, driving the switch in the position 9, the switch magnet 168 will receive current by the normally closed contacts 226 and 233 of the relays 220. 230 and the switch arm 223, driving it further to the position 11, I

in which the release of all the selectors takes placein the same manner as after a finished conversation. I

If a conversation has taken placeand both subscribers replace their receivers, the relays 220, 230 will simultaneouslv release their armatures. The switch, standing in position 10 will then receive current, as'in the previous case, by the contact 233 of the relay 230 and the switch arm 223, and will go to the position 11. In this position the switch arm 207 has broken the holding circuit of the relay 167 and by its contacts 171, 172, 17 3 and the switch arms 192, 193, 194 the three phase current from the supply circuit X, Z. Y is closed to the motor for driving the selector back to its normal position. Having reached this position the off normal switch 222 is restored to its normal position, breaking the contact 225 and closing the contact 224, thereby send ing a current through the switch ma gnet- 168 over the switch arm 223, which drives the switch to its normal position. At the same time the holding circuit of the test relay 139 of the group selector, Fig. 6, is opened by the in opening its three contacts for the adjusting circuit of the motor, in which circuit the relay 116 is included, alsoopens its contact 153 for holding therelay 84 of the line finder, Fig. 5, but as the relay 116 is arranged for a sluggish release, this relay does not at once close 'its contact 113. Thus therewill be a momentary break in the holding circuit'of the relays 84 and 70, causingthese relays to return to normal. The line finder is now ready to respond to a new call.

Inthe description of the operation of the group selector, Fig. 6, it was mentioned, that the selector, when it has found a free trunk line and is going to be stopped, may be brought back nearly three steps, by means of the adjur-iting current, if it has gone so far past the found line before the motor could be stopped, This is of course a great advan- I relay 163-as shown in" the lower left corner.

of the drawing-which, when energized in series with the test relay 139, of the group selector, closes a holding contact 247, by means of which the relay 163 is keptenergized untilthe connector in returning to normal opens the contact-225, thereby for a moment breaking the holding circuit of the relay 163. The minus potential, imposed on the test l ne 162 over a resistance 248 at the closing of the contact 247 makes the trunk line testbusy during the'time the test brush 126 leaves the test contact 129.

If a system with first and second group selectors is used, the second group selector.

may be arranged in the same way as the (first) group selector accordingtoFig, 6, but

if the arrangement for preventing double connection, just described, shall be used, the resistance 110, Fig.6, should be replaced by a relay 110 closing a holding circuit through a resistance, as shown in the lower left corner of the drawing.

Fig.8 shows a circuit diagram of a modified arrangement for starting the line finders. The object of this modification is, firstly, to economize with regard to the number of the line finders required for a certain, large group of subscribers lines, f. i. 500 or 1000 lines, secondly, to shorten the average time required for a line finder to reach the multiple contacts of a calling line and, thirdly, to reduce the number of -line finders started by a calling line. For this purpose a large group of subscribers, f. i. 500 or 1000, have access to every one of a" number of line finders required to take the calls from this group of subscribers, but, as it would be unsuitable to start such a large number of line finders for every call in this large group of lines, the starting is arranged in such a manner that, when a subscriber calls, during normal traffio only those line finders, which happen to be in the neighborhood of the multiple contacts of this subscribers line, are started.

The field of multiple contacts is divided in sections of for instance 100 lines and for each section is provided a pilot relay 271, connected to the line relays in the same way as the pilot relay 71 in Fig. 5. There is also a secondary pilot relay 274, corresponding to the secondary pilot relay 74 in Fig. 5, but the relay 274 is arranged in a different way, inasmuch as it has its contact 275 not directly connected to a number of individual starting relays of the line finders as in the previous scheme, but connected to a number of sectional contact rails 278, which are joined together, through the winding of a relay 276, provided for each section. The line finders being all common to all the lines of the multiple field, the track of every line finder must cover the whole width of the contact field or panel for the group of lines in question. But for each track the contact rail 278, which transmits the current to the individual'starting relay 281 of the line finder, is divided up in as many from each other insulated parts as there are sections of the contact field, and then all the sectional contact rails 278 of one section are oined and connected to the contact 275 of the pilot relay 274, as already mentioned.

The starting relay 281 has its winding on one side connected to the contact 85 of the relay 84, as in Fig. 5, but the other side of the winding instead of being directly connected to the starting contact of the secondary pilot relayis connected to one of the contact rails for the three phaseqcurrent, leading to one of the field coils of the motor. Alternatively the relay 281 may have three windings as shown at the bottom of the drawing, which are all oined and connected to the relay contact 85, on one side, while on the other side they are connected each to one of the three phase contact rails leading to the motor field coils.

The polarizing coil 94 of the motor armature is on one side connected to the neutral point of the field coils 91. 92, 93, as before, but on the other side the coil 94 is connected to an additional contact roller 279, which is in contact with the sectional contact rail 278 of the section where the line finder for the moment stands. It will be understood that by means of the sectional contact rails 278,

connected vertically together and to the contact 275 of the pilot relay 274, but insulated from the groups of sectional contact rails 278 of all other sections of the contact field, it is possible to limit the starting impulse, sent out by the relay 274, to only starting relays of those line finders, which happen to be standing within the section in question. The sectional contact rails 278 at the same time transmit the battery current for polarizing the armature of the motor.

As an alternative the sectional contact rails 278 may at the same time form the carrying rails for the line finders.

Fig. 8 shows the relays for the sectional contact rails of three consecutive sections, while in the middle section the motor and all the relays for the line finder are shown.

The winding of the starting relay 281 has a high resistance so as not to interfere with the three phase current.

The operation of the starting arrangement is as follows:

When a subscriber having his line contacts in the middle section is calling, his line relay will pull up and close the circuit oi the pilot relay 271 in the same way as shown in Fig. 5. The pilot relay 271 being energized, sends a current through the middle winding of the secondary pilot relay 274, which closes its contact 275, whereby all the contact rails 278 of this section are connected to earth through the winding of the relay 276, which has a low resistance. The starting relay 281 of every tree line finder standing within this section now receives a current on the following path: earth-27527627 8-27 9 94-91 (92, 93)28185-minus pole of battery. This current is very faint, owing to the high resistance of the relay 281, and has no other influence on other parts of the circuit. The relay 281 being energized, closes the three phase current for the field coils 91, 92, 93 and the direct current for the armature coil 94 of the motor and sets out plus potential on the test brush through the test relay 82 in exactly the same manner as the starting relay 81 in the previous diagram, Fig. 5. But the direct current from the battery '13, Fig. 5, inthis case does not fiow directly from the plus pole, or earth, to the armature coil 94, but it must go through the low resistance winding of the relay 276 and also pass the contact rail 278 and the contact roller 279. The relay 276 being excited by said current pulls up its armature and opens its contact 277, thereby cutting off an auxiliary starting circuit leading to a winding on each of the 1 two secondary pilot relays of the neighbouring sections. Thus the said auxiliary starting circuit remains inactive. But it the line finder shown in the middle section has moved along its track to some other section, and there is no tree line finder standing on any of the contact rails 278 of the middle section, then the relay 276 does not get any current, its contact 27 7 remains closed and a current flows instead in the auxiliary starting circuit, en

ergizing the secondary pilot relays 274 of both neighbouring sections. These relays now close their contact 275, thereby sending starting current to all free line finders standing within these two sections. These line finders now start to move to the right or to motor armature will receive its current through the winding of the relay 276 of this section which opens its contact 277, thereby withdrawing the callfor assistance to the neighbouring sections,, as will be easily understood from thediagram. 7

During normal traffic there will always be some free line finders within the section of the calling line, thus this call for assistf ance will be sent to the neighbouring sections only in case of occasional overloads of calls in some section. It is obvious that if, in such a case, it would happenthat even in one or both neighbouring sections there are no free line finders, the call for assistance will be transferred to the next section or sections by means of the relays 274 and the closed contacts 277 of the busy. sections. Thus, by means of this starting arrangement it is possible to utilize the line finders in the mosteconomical manner, because any one of all the line finders provided for a large group,

Y for instance 1000 lines, may be used for a call from any line in this large group. At the same time the time for a line finder to find a calling line, during normal traffic is reduced and unnecessary wear avoided by starting only line finders which happento stand near the calling line. I

It is well known among telephone engineers that, in most telephone systems, the group selectors may be carried out reversed, that is to say, on the line finder principle. This is of course possible also in the present system and in such a case the above described starting arrangement accordmg to Fig. 8

may be used with advantage for the group selectors as well.

Referring to the group selector and the arrangement of the impulse contacts (130) along the'track of the selector, this arrangement in connection with the fact, that the. design of the selector is independent of the length of the track, makes it possible to divide the contact fieldin groups of lines, which are quite difierent with regard to; the number of lines in each group, This is a great advantage, especially in a plant with more exchanges, because the traflic in this case is almost without exception unevenly distributed in the various directions. Thus, in one direction it may be suitable to let the group selector select on such large. groups as 5060 trunk lines, in order to economize: in the total number of trunks'required, while in some other direction 10-20 lines may be sufiicient to take the total traffic. In the latter case it would evidently be a waste of material toprovide multiple contacts. for 50-60 lines. In consequence a great deal of material and space is saved by dimensioning the sizes of the groups exactly in accordance with the trafiic requirements, which is possible in this system, because thedistance between theimpulse contacts of the groups is immaterial for the working of, the number sender and its control of'the group selector.

In order to facilitate a change in the number of lines of the various groups even since the plant has been put in trafic, impulse contacts may be provided for each 10 or 20 lines, and these contacts may then be connected or not, according to the size of the groups.

- Evidently, for the above mentioned reasons it is also possible to subsequently extend the multiple contact field of the group selectors by adding new .contact banks, either for taking in new groups of lines or for increasing the number of lines within the groups. In case more than 10 groups of trunk lines shall be arranged for in the group selector, the first digit of the subscribers number maybe a letter, and the first contact segment in the number sender may in this case be made longer so' as to take 20 to 25 letters instead of only the ten numerals.

The described telephone system and its various components may of course be modified in many other ways without departing from the features of the invention.

I claim:

1. An automatic telephone system having switches in the form of carriages, movable contacts mounted on said carriages, a, contact field, a number of tracks for said carriages arranged in front of said contact field, and alternating current motors individually allotted to said switches and mounted on the carriages.

2. An automatic telephone systemv as claimed in claim 1 in which the switches are driven by synchronous motors. V

3. An automatic telephone system as claimed in claim 1, in which the switches are driven by synchronous alternating current motors having armatures polarized by means of direct current; 4. In an automatic telephone system the combination of a number of switchesv in the form of carriages, each having an individual electric motor mounted on the carriage and 1 provided with a uniformly movable armature, movable contacts-mounted on said car-v riages, a number of superimposed horizontal tracks for said carriages, a contact field.ex-.

tending vertically-on one side of the switches, stationary contact rails extending along the t-racksand means for connect-ing said movable contacts with said contact rails.

5. A combination as claimed in claim 4 in which the movable contacts are connected with the contact rails by means of electric rollers adapted to engage the rails so as to exert an elastic lateral pressure on both sides thereof.

6. A combination as claimed in claim 4: in which the movable contacts are connected with thecont-act rails by means of rollers each consisting of two loosely pivoted discs pressed against the opposite sides of the rail so as to forma double contact with partly i rubbing and partly rolling contact surfaces.

of a contact field andto be driven each by an individual electric motor mounted on the carriage andprovided with a uniformly movable armature, and a centrifugal device operated by the movement of the carriage to withdraw the said contacts from the contact field during the movement of the carriage.

8. In an automatic telephone system the combination of a number of switches consisting of carriages adapted to run on tracks in front of a contact field and to be driven each by an individual motor mounted on the carriage and provided with a uniformly movable armature, a number of supply circuits for diiferent currents andmeans for supplying current from one or the other circuit to the motor to drive the latter at difierent speeds.

9. A combination as claimed in claim 8 in which theswitches are provided with alternating current motors adapted to be driven by alternating currents of difierent frequency.

10. In an automatic telephone system the combination of a number of switches the 1' switch.

' 11. A combination as claimed in claim 10, in which the motor consists of an alternating current motor the armature of which is provided with a polarizing winding connected at oneend to the neutral point of the star connected stator'windings of the motor and at the other end through a source of direct current to the neutral point of the star connected windings of an alternating current generator.

12. In an automatic telephone system the combination of a number of switches consisting of carriages arranged to run on tracks in front of a contact field and to be driven each by an individual alternating current motor havinga uniformly movable armature, stator and armature windings, a circuit including the stator windings, and a source of alternating current, another circuit including the armature winding and a source of direct current and means for disconnecting the source of alternating current and switcl ing the stator and armature windings to-. gether into a direct current circuit for stopping the movement of the switch.

13. A combination as claimed in claim 12, in which a test relay is adapted, upon finding a disengaged line, to disconnect the source of alternating current and to switch the stator and armature windings together intoa direct current circuit for stopping the movement of the switch.

14. In an automatic telephone system the combination of a number of switches consisting of carriages arranged torun on tracks in front of a contact fieldand to be driven each by an individual synchronous alternating current motor having a uniformly movable armature one revolution of which corresponds to a number or" contact positions of the switch equal to the number of phases used for driving the motor, or a multiple thereof, stator and armature windings, a circuit including the stator winnings and a source of alter nating phase current, another circuit includ ing the armature winding and a source of direct current, means for disconnecting the source of alternating current and switching the stator and armature windings together into a direct current circuit for stopping the movement of the switch, and a number of polarized relays arranged to work in synchronism with the alternations of the phase currents and to control the said direct current circuit so as to set up, upon said circuit being closed, a field that will cause the armature to be centered and held in a position corresponding to the contact position selected.

15. In an automatic telephone system t combination of a number of switches the movable contacts of which are mounted on carriages arranged to run on tracks in front of a contact field, and to be driven each by an individual electrical motor mounted on th carriage, a number sender for controlling the setting of the switches, and stationary contacts provided along the track and adapted to cooperate with one of the movable contacts for sending numerical control impulses back to thenumber sender.

16. A combination as claimed in claim 15, in which the stationary contacts are arranged at irregular distances from one another corresponding to the variable extension of the 

